JP4343225B2 - Solar cells - Google Patents

Description

  The present invention relates to a solar battery cell, and more particularly to a solar battery cell in which the occurrence of electrode peeling is prevented.

  Solar power generation is a clean power generation method that generates power using light energy, which is infinite energy, and does not emit harmful substances. In this solar power generation, solar cells that are photoelectric conversion elements that generate electric power by converting light energy from the sun into electrical energy are used.

  Conventionally, an electrode on the back surface of a light receiving surface in a generally produced solar battery cell is formed by printing a silver paste and an aluminum paste on the back surface of a silicon substrate by screen printing, and drying and baking. Here, aluminum formed on almost the entire back surface of the silicon substrate serves as a positive electrode. However, when producing a solar cell module, it is not possible to directly solder a tab wire for taking out an output to an aluminum electrode formed of aluminum. For this reason, a silver electrode is formed on the back surface of the silicon substrate as an output output electrode so that the silver electrode and the aluminum electrode partially overlap (see, for example, Patent Document 1 and Patent Document 2).

  Thus, on the back surface of the solar cell substrate, the aluminum electrode for increasing the output and the silver electrode for taking out the output are formed so as to partially overlap each other. And in the part which this aluminum electrode and the silver electrode overlapped, three types of metals, silicon of a silicon substrate, aluminum of an aluminum electrode, and silver of a silver electrode, are partially alloyed.

JP 2003-273378 A JP 10-335267 A

  However, the overlapped portion is very fragile due to stress that is likely to occur due to the difference in thermal expansion coefficient of each member during rapid heating and cooling during firing. For this reason, after baking, when the silver electrode has overlapped on the aluminum electrode, for example, the corner | angular part of a silver electrode may peel in this overlapping part.

  Moreover, in order to reduce the cost of the solar battery cell, it is necessary to make the silicon substrate having a high cost ratio thinner. However, if the silicon substrate is simply thinned, the warp of the silicon substrate due to the difference in thermal shrinkage between silicon and aluminum is greater in the thinned silicon substrate than in the case of the thick silicon substrate.

  When the warpage of the silicon substrate is large as described above, in the manufacturing process after firing, the silicon substrate is cracked and the production yield is lowered, or the silicon substrate is cracked and the manufacturing itself is impossible. , Etc.

  As countermeasures against these, for example, a method of reviewing the material of the aluminum paste and improving the thermal contraction rate of the electrode material to suppress the warpage of the silicon substrate can be considered. However, even if the material of the aluminum paste is simply changed, depending on the combination, peeling of a part of the silver electrode still occurs due to the difference in heat shrinkage between aluminum and silver.

  Even in this case, when the degree of peeling of the silver electrode is severe, there is a problem that the yield of the solar battery cell is reduced due to stacking of the solar battery cells and the characteristics of the solar battery cell are reduced, and the production yield is reduced. is there.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the photovoltaic cell in which peeling of the electrode was prevented effectively.

  In order to solve the above-described problems and achieve the object, a solar battery cell according to the present invention includes a photoelectric conversion layer, a first electrode formed on one side of the photoelectric conversion layer, and the other side of the photoelectric conversion layer. In the in-plane direction of the photoelectric conversion layer, the outer edge overlaps with the second electrode, and the corner is rounded to provide a substantially rectangular shape on the other surface of the photoelectric conversion layer. And a third electrode for extracting output from the second electrode.

  The solar cell according to the present invention includes a photoelectric conversion layer, a first electrode formed on one surface side of the photoelectric conversion layer, and a third electrode for taking out an output from a second electrode provided on the other surface side of the photoelectric conversion layer. In the solar cell comprising the electrode, the outer edge of the third electrode overlaps with the second electrode, and the corners of the third electrode are rounded to provide a substantially rectangular shape. Since the third electrode and the second electrode can be reliably bonded, there is an effect that it is possible to realize a solar battery cell that effectively prevents the third electrode from peeling off.

  In addition, the solar cell according to the present invention is sufficiently compatible with the silicon substrate that does not generate many substrate cracks as in the past even when the silicon substrate is thinned to reduce the cost of the solar cell. It is possible to increase the degree of freedom in selecting the type of material that can be used.

  And since the photovoltaic cell concerning this Embodiment uses the corner | angular part of a 3rd electrode as the rounding part, the area of a 3rd electrode becomes small and it can reduce the usage-amount of electrode material. Thereby, the photovoltaic cell concerning this Embodiment can aim at the reduction of material cost, and there exists an effect that an inexpensive photovoltaic cell can be implement | achieved.

1-1 is sectional drawing which shows schematic structure of the photovoltaic cell concerning Embodiment 1 of this invention. FIG. 1-2 is a plan view illustrating a schematic configuration of the surface side ((light receiving surface side) of the solar battery cell according to the first embodiment of the present invention. FIGS. 1-3 is a top view which shows schematic structure of the back surface side (surface side facing a light-receiving surface) of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 1-4 is a figure which expands and shows the alloy part periphery which three types of metals, silicon, aluminum, and silver, partly alloyed in the photovoltaic cell concerning Embodiment 1 of this invention. 1-5 expands and shows the peripheral part of the area | region B and the area | region C in which the aluminum electrode provided in the back surface of the photovoltaic cell concerning Embodiment 1 of this invention and the back surface silver electrode overlapped partially. It is sectional drawing. FIG. 2 is an enlarged cross-sectional view of a peripheral portion of a region B ′ and a region C ′ in which an aluminum electrode and a back surface silver electrode provided on the back surface of a conventional solar battery cell partially overlap each other. FIGS. 3-1 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-2 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-3 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-4 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. 3-5 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-6 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 3-7 is a top view which shows an example of the screen mask used for printing of a silver paste in manufacture of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 3-8 is sectional drawing which shows an example of the screen mask used for printing of a silver paste in manufacture of the photovoltaic cell concerning Embodiment 1 of this invention. 3-9 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. 3-10 is sectional drawing explaining the manufacturing method of the photovoltaic cell concerning Embodiment 1 of this invention. FIG. 4-1 is a plan view for explaining dimensions on the back surface side (surface side opposite to the light receiving surface) in a specific solar battery cell to which Embodiment 1 of the present invention is applied. FIGS. 4-2 is a top view for demonstrating the shape and dimension of the back surface silver electrode in the concrete photovoltaic cell to which Embodiment 1 of this invention is applied. FIGS. FIG. 5-1 is a plan view illustrating a schematic configuration of the back surface side (surface side facing the light receiving surface) of the solar battery cell according to the second embodiment of the present invention. FIG. 5-2 is an enlarged view of the vicinity of an alloy part in which three types of metals, silicon, aluminum, and silver, are partially alloyed in the solar battery cell according to the second embodiment of the present invention. FIGS. 5-3 expands and shows the peripheral part of the area | region D and the area | region E with which the aluminum electrode and back surface silver electrode which were provided in the back surface of the photovoltaic cell concerning Embodiment 2 of this invention partially overlapped. It is sectional drawing. FIG. 6-1 is a plan view for explaining dimensions on the back surface side (surface side opposite to the light receiving surface) in a specific solar battery cell to which Embodiment 2 of the present invention is applied. FIG. 6-2 is a plan view for explaining the shape and dimensions of the back surface silver electrode in a specific solar battery cell to which the second embodiment of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor layer part 11 Silicon substrate 13 N type diffused layer 13a N type diffused layer 14 p ⁺ layer 15 Antireflection film 17 Aluminum electrode 17a Aluminum paste layer 19 Back surface silver electrode 19a Silver paste layer 21 Surface silver electrode 21a Silver paste layer 23 Alloy Part 25 mesh 27 emulsion 31 backside silver electrode 33 alloy part

  Hereinafter, embodiments of a solar battery cell according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the following drawings, the scale between the drawings and the scale between the members may be different from the actual ones for easy understanding.

Embodiment 1 FIG.
FIGS. 1-1 to 1-3 are diagrams illustrating a schematic configuration of the solar battery cell according to the first embodiment of the present invention, and FIG. 1-1 illustrates a schematic configuration of the solar battery cell according to the first embodiment. It is sectional drawing shown. Moreover, FIG. 1-2 is a top view which shows schematic structure of the surface side (light-receiving surface side) of the photovoltaic cell concerning Embodiment 1, and FIGS. 1-3 is the back surface of the photovoltaic cell concerning Embodiment 1. FIG. It is a top view which shows schematic structure of the side (surface side facing a light-receiving surface). In addition, FIG. 1-1 is sectional drawing in line segment AA of FIGS. 1-3.

As shown in FIGS. 1-1 to 1-3, the solar cell according to the present embodiment includes a p-type layer 11 that is a p-type silicon substrate as a semiconductor substrate, and the conductivity of the surface of the p-type layer 11. A semiconductor layer portion 10 which is a photoelectric conversion layer including an n-type diffusion layer 13 whose type is inverted, and a p ⁺ layer (BSF layer: Back Surface Field) 14 containing a high-concentration impurity; An antireflection film 15 provided on the light receiving surface for preventing reflection of incident light, a surface silver electrode 21 which is a light receiving surface electrode portion provided in a substantially rod shape on the light receiving surface of the semiconductor layer portion 10, and power extraction and incidence For the purpose of reflecting light, an aluminum electrode 17 that is a back electrode portion provided on almost the entire back surface of the semiconductor layer portion 10, and a back silver electrode 19 that is a take-out electrode portion for taking out power from the aluminum electrode 17, Is configured with

In the solar battery cell according to the present embodiment configured as described above, sunlight is irradiated from the light receiving surface side (antireflection film 15 side) of the solar battery cell, and an internal pn junction surface (with the p-type layer 11). When it reaches the junction surface with the n-type diffusion layer 13, the holes and electrons merged at the pn junction surface are separated. The separated electrons move toward the n-type diffusion layer 13. On the other hand, the separated holes move toward the p ⁺ layer 14. As a result, a potential difference is generated between the n-type diffusion layer 13 and the p ⁺ layer 14 so that the potential of the p ⁺ layer 14 becomes high. As a result, the surface silver electrode 21 connected to the n-type diffusion layer 13 becomes a positive pole, and the aluminum electrode 17 connected to the n-type diffusion layer 13 becomes a negative pole, and a current flows through an external circuit (not shown).

Next, features of the solar battery cell according to the present embodiment will be described. As shown in FIGS. 1-3 and 1-4, in the solar cell according to the present embodiment, the aluminum electrode 17 and the back surface silver electrode 19 partially overlap on the p ⁺ layer 14. 1-4 is an enlarged view showing the periphery of the back surface silver electrode 19 in the plan view of FIG. 1-3, and the aluminum electrode 17 and the back surface silver electrode 19 provided on the back surface of the solar battery cell partially overlap each other. FIG. Moreover, FIG. 1-5 is a figure which expands and shows the back surface silver electrode 19 periphery in sectional drawing of FIG. 1-1, and the aluminum electrode 17 and the back surface silver electrode 19 provided in the back surface of the photovoltaic cell are partially. It is sectional drawing which expands and shows the peripheral part of the area | region B and the area | region C which overlapped.

In the region B and the region C where the aluminum electrode 17 and the back surface silver electrode 19 partially overlap, there are three types of silicon ^: silicon of the p ⁺ layer 14 of the silicon substrate, aluminum of the aluminum electrode 17, and silver of the back surface silver electrode 19. These metals are partially alloyed to form an alloy portion 23 as shown in FIGS. 1-4 and 1-5. In FIGS. 1-1 and 1-5, the boundaries of the respective metals (silicon, aluminum, silver) are clear for the region B and the region C, but naturally this part is partially alloyed. Therefore, it is actually unclear.

  Here, in the solar battery cell according to the present embodiment, as shown in FIGS. 1-3 and 1-4, the back surface silver electrode 19 exhibits a substantially rectangular shape (rectangle) in the in-plane direction of the silicon substrate. And the back surface silver electrode 19 exhibits a curvilinear shape at a corner portion of a substantially rectangular shape (rectangle). More specifically, the back silver electrode 19 has a substantially square (rectangular) corner as a rounded portion.

  Thereby, in the solar cell according to the present embodiment, as shown in FIG. 1-5, the alloy part 23 is reliably formed in the region B and the region C where the aluminum electrode 17 and the back surface silver electrode 19 partially overlap each other. In addition, the back silver electrode 19 and the aluminum electrode 17 are also securely bonded to the end of the back silver electrode 19.

  In the conventional solar battery cell, the shape of the back surface silver electrode 19 is substantially rectangular (rectangular) in the in-plane direction of the silicon substrate, and the corners of the substantially rectangular (rectangular) are substantially perpendicular. And also in the conventional solar cell, similarly to the solar cell according to the present embodiment, as shown in FIG. 2, the region B ′ and the region C ′ in which the aluminum electrode 17 and the back surface silver electrode 19 partially overlap each other. Have

  In such a solar battery cell, this overlapping portion is caused by stress that is likely to occur due to the difference in thermal expansion coefficient of each member, which occurs in the rapid heating process and cooling process during firing during production. , Has become very vulnerable. Therefore, in the region B ′ and the region C ′ where the aluminum electrode 17 and the back surface silver electrode 19 partially overlap after firing, as shown in the region C ′ in FIG. The back surface silver electrode 19 may peel off from the aluminum electrode 17 in some cases. This stress tends to concentrate on the sharp corners of the back surface silver electrode 19. That is, due to the concentration of the stress, the alloy portion 23 is not normally formed at the sharp corner portion of the back surface silver electrode 19, and the back surface silver electrode 19 tends to peel from the right angle portion.

  Therefore, in the solar cell according to the present embodiment, the corners are rounded so as to eliminate the sharp corners of the back surface silver electrode 19 so that stress is not concentrated on the corners of the back surface silver electrode 19. Thereby, in the solar cell concerning this Embodiment, the stress concentrated on the corner | angular part of the back surface silver electrode 19 can be relieved, and as shown to FIGS. 1-5, the aluminum electrode 17 and the back surface silver electrode 19 and In the region B and the region C where are partially overlapped, the alloy part 23 is reliably formed, and the bonding force between the aluminum electrode 17 and the back surface silver electrode 19 and the substrate bonding force of the aluminum electrode 17 and the back surface silver electrode 19 are improved. Therefore, according to the solar battery cell according to the present embodiment, the back surface silver electrode 19 and the aluminum electrode 17 are reliably bonded even at the corners of the back surface silver electrode 19 to effectively prevent the back surface silver electrode 19 from peeling off. It is possible to realize the solar battery cell.

  When the rounding dimension R is larger than the dimension of the alloy part 23, a part of the alloy part of the aluminum electrode 17 and the back surface silver electrode 19 cannot be formed, which is inappropriate as the back surface silver electrode 19. . Therefore, as shown in FIGS. 1-4, the dimension L1, L3 of the part which determines the dimension of the alloy part 23, and the aluminum electrode 17 and the back surface silver electrode 19 overlap in the long side direction of the back surface silver electrode 19, and an aluminum electrode The values of the dimensions L5 and L7 of the portion where 17 and the back surface silver electrode 19 overlap in the short side direction of the back surface silver electrode 19 need to be determined so that the alloy part 23 can be formed reliably. In addition, the aluminum electrode 17 and the back surface silver electrode 19 are formed by screen printing as will be described later. However, the above dimensions should be determined in consideration of misalignment during printing of the aluminum paste and the silver paste.

  In addition, in the conventional solar cell, when the silicon substrate is made thin to reduce the cost of the solar cell, the thermal contraction rate between silicon and aluminum compared to the case where the thick silicon substrate is used. The warpage of the silicon substrate due to the difference is increased. And, when the warpage of the silicon substrate occurs greatly, in the manufacturing process after firing, the silicon substrate is cracked and the production yield is reduced, or the manufacturing itself is impossible due to the crack of the silicon substrate. Problems occur.

  As countermeasures against these, even when the material of the aluminum electrode is changed to improve the thermal contraction rate of the electrode material and suppress the warpage of the silicon substrate, the difference in thermal contraction rate between aluminum and silver depends on the combination of materials. From this, peeling occurs on a part of the back surface silver electrode. And when the degree of peeling of the back surface silver electrode is severe, it leads to the generation of cracks in the solar cells due to the stacking of the solar cells and the deterioration of the characteristics of the solar cells, leading to a problem that the production yield is reduced.

  However, in the solar cell according to the present embodiment, as described above, the bonding force between the aluminum electrode 17 and the back surface silver electrode 19 formed on the back surface of the silicon substrate, the silicon substrate of the aluminum electrode 17 and the back surface silver electrode 19 And the peeling of the back surface silver electrode 19 or the peeling of the aluminum electrode 17 can be effectively prevented. Thereby, the joining between the aluminum electrode 17 and the back surface silver electrode 19 and the joining of the aluminum electrode 17 and the back surface silver electrode 19 to the substrate can be ensured.

  Therefore, according to the solar cell according to the present embodiment, even when the silicon substrate is thinned to reduce the cost of the solar cell, many substrate cracks may occur in the silicon substrate as in the past. Therefore, it is possible to cope with the problem, and it is possible to increase the degree of freedom in selecting the type of silver paste that can be used.

  Furthermore, in the solar cell according to the present embodiment, since the sharp corner portion where the back surface silver electrode should exist in the conventional solar cell is a rounded portion, the area of the back surface silver electrode 19 is reduced. The amount of silver paste used for the back surface silver electrode 19 is reduced. Therefore, according to the solar cell according to the present embodiment, it is possible to reduce the material cost and to achieve an effect that an inexpensive solar cell can be realized. The specific reduction effect of the silver paste will be described later.

  Below, the manufacturing method of the photovoltaic cell concerning this Embodiment comprised as mentioned above is demonstrated. In order to manufacture the solar battery cell according to the present embodiment, first, as shown in FIG. 3-1, for example, a p-type single crystal silicon ingot manufactured by a pulling method, or a polycrystalline manufactured by a casting method. A p-type silicon substrate 11 ′ is sliced from the silicon ingot. Then, for example, caustic soda or carbonated caustic soda of about several wt% to 20 wt% is etched away by a thickness of about 10 μm to 20 μm to remove a damage layer or contamination on the silicon surface that occurs when slicing.

  Further, if necessary, the substrate is washed with a mixed solution of hydrochloric acid and hydrogen peroxide to remove heavy metals such as iron adhering to the substrate surface. Thereafter, anisotropic etching is performed with a solution obtained by adding IPA (isopropyl alcohol) to a similar alkaline low concentration solution, and a texture is formed so that, for example, a silicon (111) surface is exposed.

Next, an n-type diffusion layer 13a is formed to form a pn junction. In this n-type diffusion layer 13a formation process, for example, phosphorus oxychloride (POCl ₃ ) is used, and diffusion treatment is performed in a mixed gas atmosphere of nitrogen and oxygen at 800 ° C. to 900 ° C., as shown in FIG. 3-2. An n-type diffusion layer 13a in which the conductivity type is inverted by thermally diffusing phosphorus is formed on the entire surface of the silicon substrate 11 ′. The sheet resistance of the n-type diffusion layer 13a is, for example, several tens (about 30 to 80 to Ω / □), and the depth of the n-type diffusion layer 13a is, for example, about 0.3 to 0.5 μm.

  Next, in order to protect the n-type diffusion layer 13a on the light receiving surface side, a resist is formed by printing and drying a polymer resist paste by a screen printing method. Then, for example, the n-type diffusion layer 13a formed on the back and side surfaces of the silicon substrate 11 'is removed by dipping in a 20 wt% potassium hydroxide solution for several minutes. Thereafter, the resist is removed with an organic solvent to obtain a silicon substrate 11 'on which the n-type diffusion layer 13 is formed on the entire surface (light receiving surface) as shown in FIG.

Next, as shown in FIG. 3-4, an antireflection film 15 such as a silicon oxide film, a silicon nitride film, or a titanium oxide film is formed on the surface of the n-type diffusion layer 13 with a uniform thickness. For example, in the case of a silicon oxide film, the antireflection film 15 is formed by a plasma CVD method using SiH ₄ gas and NH ₃ gas as raw materials at a heating temperature of 300 ° C. or higher and under reduced pressure. The refractive index is, for example, about 2.0 to 2.2, and the optimum film thickness of the antireflection film 15 is about 70 nm to 90 nm.

  Next, using a screen printing method, an aluminum paste containing glass is printed and dried on the entire back surface (surface opposite to the light receiving surface) of the silicon substrate 11 ′ as shown in FIG. An aluminum paste layer 17a is formed on the entire back surface of '. In the aluminum paste layer 17 a, an opening is provided corresponding to the formation site of the back surface silver electrode 19. The coating thickness of the aluminum paste can be adjusted by the wire diameter forming the screen mask, the emulsion thickness, and the like.

  Next, using a screen printing method, a silver paste for the back surface silver electrode 19 is printed and dried on the back surface (surface opposite to the light receiving surface) of the silicon substrate 11 ′ on which the aluminum electrode 17 is formed as shown in FIG. 3-6. Then, a silver paste layer 19a is formed. At this time, the shape of the silver paste layer 19a is a substantially quadrangular (rectangular) shape with rounded corners as shown in FIG. Here, the silver paste can be printed using, for example, a screen mask patterned with the emulsion 27 on the mesh 25 as shown in FIGS. 3-7 and 3-8.

  Further, using a screen printing method, a silver paste for the surface silver electrode 21 is printed on the surface (light-receiving surface) of the silicon substrate 11 ′ on which the antireflection film 15 is formed, and dried, as shown in FIG. A paste layer 21a is formed. The coating thickness of the silver paste can also be adjusted by the wire diameter of the mesh forming the screen mask, the emulsion thickness, and the like.

  Next, in the firing step for electrode formation, the front and back electrode paste layers are simultaneously fired at 600 ° C. to 900 ° C. for several minutes to ten and several minutes. On the surface (light-receiving surface) side of the silicon substrate 11 ′, the silver paste layer is baked to become the surface silver electrode 21 as shown in FIG. 3-10, but in the silver paste while the antireflection film 15 is melted. The silver material comes into contact with the silicon of the silicon substrate 11 ′ and resolidifies. Thereby, conduction between the surface silver electrode 21 and silicon is ensured. Such a process is generally called a fire-through method.

On the other hand, on the back surface (surface opposite to the light receiving surface) of the silicon substrate 11 ′, the aluminum paste layer is baked to form the aluminum electrode 17 as shown in FIG. 3-10, and the silver paste layer is baked to form FIG. As shown in FIG. Here, aluminum in the aluminum paste reacts with silicon on the silicon substrate 11 ′ to form a p ⁺ layer 14 immediately below the aluminum electrode 17. This layer is generally called a BSF (Back Surface Field) layer and contributes to the improvement of the energy conversion efficiency of the solar cell. In the silicon substrate 11 ′, a region sandwiched between the n-type diffusion layer 13 and the p ⁺ layer 14 becomes the p-type layer 11.

  Further, the silver paste reacts directly with silicon on the silicon substrate 11 ′ where it is in direct contact with the silicon substrate 11 ′, and silicon and aluminum paste (aluminum electrode 17) on the silicon substrate 11 ′ where it is in contact with the aluminum paste. ) And the silver of the back surface silver electrode 19 partially form an alloy. Through the above steps, the cell is completed by the solar cell manufacturing process. In the module manufacturing process after the cell manufacturing process, a copper tab wire for taking out the output to the outside is disposed on the silver electrode 3.

  The above-described solar cell can be realized only by changing the shape of the back surface silver electrode, and without changing the existing equipment, the mask shape can be changed during screen printing of the silver paste for the back surface silver electrode. Can only be realized.

  Next, the reduction area of the back surface silver electrode and the reduction amount of the silver paste will be described with specific examples. Here, as shown in FIG. 4A and FIG. 4B, an example will be described in which the back surface silver electrodes 19 adjacent to each other constitute solar cells arranged in two rows in the vertical direction under the following conditions.

-Long side length L1 of the back surface silver electrode 19 = 9.8 mm
・ Short side length L5 of the back surface silver electrode 19 = 7.8 mm
・ Distance L9 = 75mm between backside silver electrode rows
-Distance L11 = 135mm between backside silver electrodes 19 at both ends in the backside silver electrode array
-Distance L13 = 22.5 mm between adjacent backside silver electrodes 19 in the backside silver electrode row

  In the solar cell having the dimensions as described above, the reduction area of the back surface silver electrode 19 when the radius of curvature R of the rounded portion of the back surface silver electrode 19 is changed from 1.0 mm to 3.0 mm in 0.5 mm increments. The silver paste reduction rate is shown in Table 1.

As shown in Table 1, as the radius of curvature R of the rounded portion of the back surface silver electrode 19 is increased from 1.0 mm to 3.0 mm, the reduced area (mm ² ) of the back surface silver electrode 19 is from 0.9 mm ² to 7. Increased to 7 mm ² . And the silver paste reduction rate (%), that is, the reduction effect of the silver paste increases from 1.1% to 10.1%. Thereby, by applying the present invention, the amount of silver paste for the back surface silver electrode 19 can be reduced, and in the solar cell according to the present embodiment, the material cost can be reduced. It can be said that a battery cell can be realized.

Embodiment 2. FIG.
In the second embodiment, another embodiment of the solar battery cell according to the present invention will be described. The basic configuration of the solar cell according to the second embodiment is the same as that of the solar cell according to the first embodiment described above. Therefore, the difference between the solar battery cell according to the second embodiment and the solar battery cell according to the first embodiment will be described below. In the following drawings, members similar to those of the solar battery cell according to the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  5A to 5C are schematic diagrams illustrating the configuration of the solar battery cell according to the second embodiment of the present invention. FIG. 5-1 is a diagram corresponding to FIG. 1-3, and is a plan view illustrating a schematic configuration of the back surface side (surface side facing the light receiving surface) of the solar cell according to the second embodiment. Moreover, FIG. 5-2 is a figure corresponding to FIGS. 1-4, is a figure which expands and shows the back surface silver electrode 31 periphery in the top view of FIG. 5-1, and is provided in the back surface of the photovoltaic cell. It is a figure which expands and shows the part which the electrode 17 and the back surface silver electrode 31 overlapped partially.

  And FIG. 5-3 is a figure corresponding to FIG. 1-5, is a figure which expands the back surface silver electrode 31 periphery, and shows the aluminum electrode 17 and back surface silver electrode 31 which were provided in the back surface of the photovoltaic cell. It is sectional drawing which expands and shows the peripheral part of the area | region D and the area | region E which overlapped partially. In addition, since the cross-sectional structure of the photovoltaic cell according to the first embodiment and the schematic configuration on the light receiving surface side (front surface side) of the photovoltaic cell are the same as those in the first embodiment, FIGS. 2 will be referred to.

  Here, the back surface silver electrode 31 in the present embodiment corresponds to the back surface silver electrode 19 in the first embodiment, and the corners are not rounded portions as shown in FIGS. 5A and 5B. It is different from the case of Embodiment 1 in that it is a chamfered portion.

  Here, in the solar cell according to the present embodiment, as shown in FIGS. 5A and 5B, the back surface silver electrode 31 exhibits a substantially rectangular shape (rectangle) in the in-plane direction of the silicon substrate. The back silver electrode 31 has a substantially square (rectangular) corner as a chamfer.

In addition, although the shape of the corner of the back surface silver electrode is different from that in the first embodiment, in regions D and E where the aluminum electrode 17 and the back surface silver electrode 31 partially overlap, p ^{+ of} the silicon substrate is formed ^. Three types of metals, silicon of the layer 14, aluminum of the aluminum electrode 17, and silver of the back surface silver electrode 31, are partially alloyed to form an alloy portion 33 as shown in FIGS. 5-2 and 5-3. . In FIG. 5C, the boundaries of the respective metals (silicon, aluminum, silver) are clear for the region D and the region E, but naturally this part is partially alloyed, so in practice , Has become unclear.

  Thereby, in the solar cell according to the present embodiment, the alloy part 33 is reliably formed in the region D and the region E where the aluminum electrode 17 and the back surface silver electrode 31 partially overlap as shown in FIG. In addition, the back silver electrode 31 and the aluminum electrode 17 are reliably bonded also at the end of the back silver electrode 31.

  In the solar cell according to the present embodiment, the corners are chamfered so as to eliminate the sharp corners of the backside silver electrode 31 so that stress is not concentrated on the corners of the backside silver electrode 31. Thereby, in the photovoltaic cell concerning this Embodiment, the stress concentrated on the corner | angular part of the back surface silver electrode 31 can be relieve | moderated, and as shown to FIGS. 5-3, the aluminum electrode 17 and the back surface silver electrode 31 and In the region D and the region E where are partially overlapped, the alloy part 33 is reliably formed, and the bonding force between the aluminum electrode 17 and the back surface silver electrode 31 and the substrate bonding force of the aluminum electrode 17 and the back surface silver electrode 31 are improved. Therefore, according to the solar battery cell according to the present embodiment, the back surface silver electrode 19 and the aluminum electrode 17 are reliably bonded even at the corners of the back surface silver electrode 19 to effectively prevent the back surface silver electrode 19 from peeling off. It is possible to realize the solar battery cell.

  In addition, when the chamfer dimension C is larger than the dimension of the alloy part 33, a part of the alloy part of the aluminum electrode 17 and the back surface silver electrode 31 cannot be formed, which is inappropriate as the back surface silver electrode 31. Therefore, as shown in FIG. 5B, the dimensions L21 and L23 of the portion where the aluminum electrode 17 and the back surface silver electrode 31 overlap in the long side direction of the back surface silver electrode 31 and the aluminum electrode which determine the dimensions of the alloy part 33 The values of the dimensions L25 and L27 of the portion where 17 and the back surface silver electrode 31 overlap in the short side direction of the back surface silver electrode 31 need to be determined so that the alloy part 33 can be formed reliably. In addition, the aluminum electrode 17 and the back surface silver electrode 31 are formed by screen printing as will be described later. However, the above dimensions should be determined in consideration of misalignment during printing of the aluminum paste and the silver paste.

  Further, also in the solar battery cell according to the present embodiment, as described above, the bonding between the aluminum electrode 17 and the back surface silver electrode 31 and the bonding between the aluminum electrode 17 and the back surface silver electrode 31 are ensured. be able to. Therefore, even in the solar cell according to the present embodiment, even when the silicon substrate is thinned to reduce the cost of the solar cell, many substrate cracks do not occur in the silicon substrate as in the past. It is possible to sufficiently cope with this, and it is possible to increase the degree of freedom in selecting the type of silver paste that can be used.

  Further, also in the solar cell according to the present embodiment, the conventional silver solar cell has a chamfered portion with a sharp corner where the back surface silver electrode should exist, and thus the area of the back surface silver electrode is reduced, and the back surface The amount of silver paste used for the silver electrode 31 is reduced. Therefore, the solar battery cell according to the present embodiment also has an effect that the material cost can be reduced and an inexpensive solar battery cell can be realized.

  In addition, the photovoltaic cell concerning this Embodiment is implemented except making it a substantially square (rectangle) by which the corner | angular part was made into a chamfer as shown in FIG. 5-1, when screen-printing a silver paste layer. It can be manufactured in the same process as in the case of Form 1. The solar battery cell according to the present embodiment can also be realized only by changing the shape of the back surface silver electrode, and at the time of screen printing of the silver paste for the back surface silver electrode without changing the existing equipment. This can be realized only by changing the mask shape.

  Next, the reduction area of the back surface silver electrode and the reduction amount of the silver paste will be described with specific examples. Here, as shown in FIG. 6A and FIG. 6B, an example will be described in which solar battery cells in which adjacent back surface silver electrodes 31 are arranged in two rows in the vertical direction under the following conditions are described.

・ Long side length L21 of the back surface silver electrode 31 = 9.8 mm
・ Short side length L25 of the back surface silver electrode 31 = 7.8 mm
・ Distance L9 = 75mm between backside silver electrode rows
-Distance L11 = 135mm between backside silver electrodes 31 at both ends in the backside silver electrode array
-Distance L13 = 22.5 mm between adjacent back surface silver electrodes 31 in the back surface silver electrode row

  In the solar cell having the dimensions as described above, the reduction area and silver of the back surface silver electrode 31 when the chamfer dimension C of the chamfered portion of the back surface silver electrode 31 is changed from 1.0 mm to 3.0 mm in 0.5 mm steps. Table 2 shows the paste reduction rate.

As shown in Table 2, as the chamfered dimension C of the chamfered portion of the back surface silver electrode 31 is increased from 1.0 mm to 3.0 mm, the reduction area (mm ² ) of the back surface silver electrode 31 is 2.0 mm ² to 18.0 mm. ^It has increased to ² . And the silver paste reduction rate (%), that is, the reduction effect of the silver paste increases from 2.6% to 23.5%. Thereby, by applying the present invention, the amount of silver paste for the back surface silver electrode 31 can be reduced, and in the solar battery cell according to the present embodiment, the material cost can be reduced, and the inexpensive solar It can be said that a battery cell can be realized.

  In both cases of Embodiment 1 and Embodiment 2, in order to obtain a reduction effect of more silver paste, it is necessary to increase the curvature radius or chamfer dimension, but if too large, aluminum and It becomes impossible to form an alloy part with silver. When selecting the actual radius of curvature or chamfer dimension, it is necessary to determine the radius of curvature and chamfer dimension so that the alloy part can be formed reliably, taking into account misalignment during printing of paste for aluminum and silver electrodes. is there.

  Moreover, the solar battery cell according to the first and second embodiments is an example of the embodiment of the present invention, and the present invention is not limited by the above description and does not depart from the gist of the present invention. The range can be changed as appropriate.

  As described above, the solar cell according to the present invention is useful for a solar cell having a structure in which an aluminum electrode and a silver electrode for output extraction partially overlap.

Claims (4)

A photoelectric conversion layer;
A first electrode provided on one side of the photoelectric conversion layer;
A second electrode provided on the other surface side of the photoelectric conversion layer;
On the other surface side of the photoelectric conversion layer, in the in-plane direction of the photoelectric conversion layer, an outer edge portion is overlapped with the second electrode and a corner portion thereof is provided in a substantially rectangular shape as a rounded portion. A third electrode for extracting the output;
A solar battery cell comprising: The second electrode is an aluminum electrode;
The third electrode is a silver electrode;
The solar battery cell according to claim 1. A photoelectric conversion layer;
A first electrode provided on one side of the photoelectric conversion layer;
A second electrode provided on the other surface side of the photoelectric conversion layer;
On the other surface side of the photoelectric conversion layer, in the in-plane direction of the photoelectric conversion layer, an outer edge portion is overlapped with the second electrode and a corner portion thereof is provided in a substantially rectangular shape as a chamfered portion, and is output from the second electrode. A third electrode for taking out
A solar battery cell comprising: The second electrode is an aluminum electrode;
The third electrode is a silver electrode;
The solar battery cell according to claim 3.

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